Proposed work includes the following: 1. Efforts to cultivate JC virus in cells other than human fetal glial cells. 2. Study of human populations in an effort to recognize primary human infections caused by JC and BK viruses. 3. Study of transformation of cells by JC virus. 4. Expansion of studies aimed at detection of JC virus genome in animal and human tumors. BIBLIOGRAPHIC REFERENCES: Quay, W. B., Ma, Y., Varakis, J. N., ZuRhein, G. M., Padgett, B. L., Walker, D.L., 1977. Modification of hydroxyindole-O-methyltransferase activity in experimental pineocytomas induced by a human papovavirus (JC). J. Natl. Cancer Inst. 58:123-127. Padgett, B. L., Rogers, C. M., Walker, D. L., 1977. JC virus, a human polyomavirus associated with progressive multifocal leukoencephalopathy: Additional biological characteristics and antigenic relationships. Infection and Immunity 15:656-662.